Process for making sintered iron base shaped bodies containing copper and tin with a tempering step followed by slow cooling

ABSTRACT

Sintered shaped bodies are made of a pulverulent mixture of tin, copper and predominantly iron by sintering the mixture in which tin is present in an amount between 0.5 and 4.5%, copper is present in an amount of 0.3 to 7%, balance iron, and wherein the ratio of tin to copper is between 1 : 0.7 and 1 : 1.5. The formed sintered body is then cooled to for instance room temperature and thereafter subjected to a tempering treatment at a temperature between 750* and 600*C followed by cooling to room temperature. The cooling after the heat treatment and preferably also the cooling after sintering are effected at a slow rate at least within the range between 750* and 300*C, that is, at a rate not exceeding 15*C per minute.

Elnited States Patent Esper et a1.

[ Dec. 10, 1974 PROCESS FOR MAKING SINTERED IRON BASE SHAPED BODIES CONTAINING COPPER AND TIN WITH TEMPERING STEP FOLLOWED BY SLOW COOLING Inventors: Friedrich Josef Esper, Leonberg;

Robert Zeller, Stuttgart, both of Germany Robert Bosch GmbH, Stuttgart, Germany Filed: Sept. 29, 1972 Appl. No.: 293,374

Assignee:

Foreign Application Priority Data Oct. 1, 1971 Germany 2149147 References Cited UNITED STATES PATENTS 3/1972 Fuchs et a1. 75/214 Primary ExaminerBenjamin R. Padgett Assistant ExaminerB. Hunt Attorney, Agent, or FirmMichael S. Striker Sintered shaped bodies are made of a pulverulent mixture of tin, copper and predominantly iron by sintering the mixture in which tin is present in an amount between 0.5 and 4.5%, copper is present in an amount of 0.3 to 7%, balance iron, and wherein the ratio of tin to copper is between 1 2 0.7 and 1 1.5. The formed sintered body is then cooled to for instance room temperature and thereafter subjected to a tempering treatment at a temperature between 750 and 600C followed by cooling to room temperature. The cooling after the heat treatment and preferably also the cooling after sintering are effected at a slow rate at least within the range between 750 and 300C, that is, at a rate not exceeding 15C per minute.

ABSTRACT 6 Claims, No Drawings PROCESS FOR MAKING SINTERED IRON BASE SHAPED BODIES CONTAINING COPPER AND TIN WITH A TEMPERING STEP FOLLOWED BY SLOW COOLING BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION The invention resides in the fact that the shaped parts after sintering are subjected to a heat treatment in the range of between about 750 and 600C and that furthermore and rate of cooling following the heat treatment is slow and particularly is slow in the range between 750 and 300C. Preferably the cooling rate should not exceed the speed of 15C per minute. Preferably this applies also to the cooling after sintering.

DETAILS OF THE INVENTION AND SPECIFIC EMBODIMENTS Preferably the heat or tempering treatment is of a duration of at least minutes. Particularly good values for the tensile strength and the elongation to fracture are obtained if the cooling speed does not exceed C per minute at any place in the range between 750 and 300C. It is therefore also preferable that the cooling from the sintering temperature at, e.g., between 900 and l,l00C down to the temperature of the heat treatment likewise is carried out at a slow rate and preferably at the rate which does not exceed the just indicated speed.

It is preferred to cool the bodies after sintering down to room temperature prior to the heat treatment. It is likewise preferred if the slow rate of cooling is observed throughout the cooling to room temperature following the sintering temperature and then again throughout the cooling from the temperature of the tempering treatment down to room temperature.

The process of the invention permits obtaining shaped bodies which in addition to adequate values of tensile strength have an excellent elongation at fracture. Shaped bodies made by the process of the invention are therefore competitive with similar bodies made from sintered alloys in which instead of tin, nickel has been used. Tin alloys, however, have the advantage over these nickel containing alloys that they can be made at a substantially lower sintering temperature. This, therefore, decreases the manufacturing cost.

The invention is further illustrated by the following Examples.

In all these Examples a pulverulent mixture was employed as the starting product which contained 2% tin, 3% copper, balance iron. The different steps listed in each of the following Examples are successive steps in each case. In each case the tensile strength and elongation at fracture has been determined at the end of the process and is indicated by the term 0 for the tensile strength and the symbol 8 for the elongation.

The term chilling when used in the Examples implies a rate of cooling at a speed in excess of 25C/min.

Examples 2 and 4 show the lower values obtained by departing from the desired optimum operation.

In a few cases intermediate values of the tensile strength and elongation after sintering and prior to the tempering treatment have also been shown to illustrate the subsequent improvement of the properties due to the tempering treatment and slow rate of cooling.

EXAMPLE 1 Sintering to the desired shape: 20 min. at 950C Cooling: to room temperature at a speed 15C/min.

0' 35 kp/mm 5 1.5%

Tempering: 2 hrs. at 650C Cooling at a speed: 15C/min.

0' 28 kp/mm 8 2 6.5%

EXAMPLE 2 Sintering: as in Example 1 Cooling: to 750C at a speed 20C/min. Chilling o 17 kp/mm 5 0.5% Tempering: 2 hrs. at 650C Cooling: at a speed 15C/min.

EXAMPLE 3 Sintering: as in Example 1 I Cooling: to room temperature at a speed 15C/min. Tempering: 1 hr. at 650C Cooling: to room temperature at a speed 15C/min. 0' 29 kp/mm 6 8.5%

EXAMPLE 4 Sintering: as in Example 1 v Cooling: to room temperature at a speed 15C/min. Tempering: 2 hr. at 650C Chilling 0,; 22 kp/mm? 8 0.5%

EXAMPLE 5 Sintering: as in Example 1 Cooling: to room temperature at a speed 15C/min. Tempering: 15 min. at 650C Cooling: at a speed 15C/min. 0' 29 kp/mm 8 8.5%

EXAMPLE 6 Sintering: as in Example 1 Cooling: to 720C at a speed 10C/min.

Tempering: 10 min. at 720C Cooling: at a speed 10C/min.

(r 29 kp/mm 6 6.5%

These examples show that essential for the invention is the heat or tempering treatment plus the slow cooling and that particularly the maximum of the cooling speed must be strictly observed in the temperature range be tween 750 and 300C.

Example 2 shows that if the cooling speed is higher after sintering, that is if at that point the rules given herein are not strictly observed even a subsequent tempering treatment and slow cooling after that treatment cannot restore the desirably high values which are for instance obtained in Example 1 and some of the other Examples. The values obtained are definitely lower, particularly for the elongation, if the cooling after sintering has been carried out at a high speed. The mere fact that there was some limitation on the cooling rate down to 750C did not help since following this temperature level there was chilling down to room temperature at a much higher speed.

Example 4 also shows that where a higher rate of cooling is carried out after the tempering treatment this will very substantially impair the values obtained, particularly the elongation value, irrespective of the fact that the alloy following the sintering was cooled at a slow rate, that is at a rate not exceeding C/min.

It is therefore preferred to cool the shaped body, after sintering at 900 to 1,100C, to room temperature at the indicated slow rate, then subject the body to the tempering treatment between 750 and 600C and again cool it to room temperature at the specified slow rate of cooling.

While this is the preferred form of the invention the critical range for the cooling rate appears to be between 750 and 300C.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention, and therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. The process of making a sintered shaped body comprising liquid phase sintering of a body consisting of a compacted pulverulent mixture of 0.5 to 4.5% tin, 0.3 to 7% copper, balance iron, the ratio of tin to copper being between 1 0.7 and l 1.5, so as to form a sintered body, tempering said sintered body at a tempering temperature between substantially 600 and 750C; and cooling said body from said tempering temperature to room temperature, said step of cooling being carried out at a rate of at most about l5C/min at least in the temperature range between said tempering temperature and approximately 300C.

2. In a process as defined in claim 1, wherein said body is sintered at a sintering temperature in excess of 750C; further comprising the steps of cooling said body from said sintering temperature to room temperature, said step of cooling from said sintering tempera ture being carried out at a rate of at most about 15C/min at least in the temperature range between about 750 and 300C; and heating said body to said tempering temperature.

3. In a process as defined in claim 1, wherein said body is sintered at a sintering temperature in excess of said tempering temperature; and further comprising the step of cooling said body from said sintering temperature to said tempering temperature at a rate of at most about 15C/min.

4. In a process as defined in claim 1, wherein said step of cooling is carried out at said rate from said tempering temperature to room temperature.

5'. In a process as defined in claim 1, wherein said step of tempering is carried out for a period in excess of about 5 minutes.

6. In a process as defined in claim 1, wherein said body is sintered at a sintering temperature between substantially 900 and l,100C 

1. THE PROCESS OF MAKING A SINTERED SHAPED BODY COMPRISING LIQUID PHASE SINTERING OF A BODY CONSISTING OF A COMPACTED PULVERENT MITURE OF 0.5 TO 4.5% TIN, 0.3 TO 7% COPPER, BALANCE IRON, THE RATIO OF TIN TO COPPER BEING BETWEEN 1 : 0.7 AND 1 : 1.5, SO AS TO FORM A SINTERED BODY, TEMPERING SAID SINTERED BODY AT A TEMPERING TEMPERATURE BETWEN SUBSTANTIALLY 600* AND 750*C; AND COOLING SAID BODY FROM SAID TEMPERING TEMPERATURE TO ROOM TEMPERATURE, SAID STEP OF COOLING BEING CARRIED OUT AT A RATE OF AT MOTS ABOUT 15*C/MIN AT LEAST IN THE TEMPERATURE RANGE BETWEEN SAID TEMPRING TEMPERATURE AND APPROXIMATELY 300*C.
 2. In a process as defined in claim 1, wherein said body is sintered at a sintering temperature in excess of 750*C; further comprising the steps of cooling said body from said sintering temperature to room temperature, said step of cooling from said sintering temperature being carried out at a rate of at most about 15*C/min at least in the temperature range between about 750* and 300*C; and heating said body to said tempering temperature.
 3. In a process as defined in claim 1, wherein said body is sintered at a sintering temperature in excess of said tempering temperature; and further comprising the step of cooling said body from said sintering temperature to said tempering temperature at a rate of at most about 15*C/min.
 4. In a process as defined in claim 1, wherein said step of cooling is carried out at said rate from said tempering temperature to room temperature.
 5. In a process as defined in claim 1, wherein said step of tempering is carried out for a period in excess of about 5 minutes.
 6. In a process as defined in claim 1, wherein said body is sintered at a sintering temperature between substantially 900* and 1,100*C. 